1. Field of the invention
The present invention relates to an electron-emitting device applied to a flat type image display apparatus and an image display apparatus fabricated by using the electron-emitting device.
2. Description of the Related Art
A surface conduction electron-emitting device uses a phenomenon in which electrons are emitted by passing a current through a small-area conductive film formed on a substrate in parallel to the film surface and such a conductive film generally has an electron-emitting portion formed by energization (forming) in advance. That is, a DC voltage or a very slowly rising voltage of about 1 V/min is applied to both ends of the conductive film to locally break, deform, or degenerate the conductive film, and thereby form an electron-emitting portion in an electrically high-resistance state. The electron-emitting portion has a crack produced in part of the conductive film and electrons are emitted from around the crack.
The surface conduction electron-emitting device has a simple structure and is easy to manufacture and therefore, a large number of devices can advantageously be arranged in a large area. Thus, various applications making use of this feature are now under study. The applicant concerned has proposed, as a manufacturing method of a surface conduction electron-emitting device advantageous for a large area, a method of forming a conductive film without relying on the sputtering method or evaporation method using a vacuum. An example thereof is a method by which a solution containing organic metal is applied onto a substrate by a spinner and then, the solution is patterned to a desired shape and the organic metal is pyrolytically decomposed to obtain a conductive film made of fine particles. Further, the applicant concerned has proposed in Japanese Patent Application Laid-Open No. 8-171850 a method by which a conductive film of a desired shape is formed by applying droplets of a solution containing organic metal onto a substrate by the inkjet method such as the bubblejet (registered trademark) method and the piezojet method.
A conductive film formed according to one of the above methods is a film made of fine particles of metal or metallic oxide or a highly continuous film. The conductive film is controlled to a desired range of resistance as an electron-emitting device by controlling component materials and a thickness thereof, but is required to be a thin film of several nm to several tens of nm from the viewpoint of the forming process and electron emission efficiency. Fluctuations in resistance of a conductive film need to be suppressed, though the film is thin, from the viewpoint of stability of electron emission characteristics and suppression of fluctuations. In addition, the conductive film is required to have high resistance of about 10 kΩ/sq to several hundreds of kΩ/sq as sheet resistance.
However, a conductive film formed according to one of the above methods and having metal as a main component cannot be used because, if the thickness thereof is several nm or less, resistance thereof fluctuates wildly. If the conductive film has a thickness of several nm or more showing stable resistance, only a low-resistance film of several kΩ/sq or less as sheet resistance can be obtained. If a conductive film is mainly made of metallic oxide and has a thickness of several nm or less, such a thin film cannot be used either because resistance thereof fluctuates wildly. Further, if the conductive film has a thickness of several nm or more showing stable resistance, resistance thereof fluctuates wildly depending on whether moisture or the like is adsorbed on the surface. Even if stabilizing treatment such as vacuum baking is performed, a portion of the film is reduced. Thus, a conductive film of high resistance of about 10 kΩ/sq to several hundreds of kΩ/sq as sheet resistance with stability could not be obtained. Therefore, a problem sometimes arises that electron emission characteristics fluctuate significantly when an electron source in which a plurality of the electron-emitting devices is arranged is used. Also in an image display apparatus constructed by arranging the electron source and an image-forming member such as a phosphor opposite to each other, fluctuations in electron emission characteristics sometimes leads to degradation in image quality, causing a problem.